Because leukemia starts in the bone marrow and often has spread to other organs by the time it is detected, there is no need for traditional staging. Instead, physicians rely upon cellular classification systems to identify the type and subtype of leukemia. Cell classification systems, in turn, help to predict the prognosis and/or outcome, of specific forms of leukemia and the likely response of treatment.

The most popular classification method for acute leukemia is the French-American-British (FAB) system—acute leukemia is divided into eight subtypes of acute myelogenous leukemia (AML) and three subtypes of acute lymphocytic leukemia (ALL). FAB originally was based upon the microscopic appearance of leukemia cells.

Chronic lymphocytic leukemia (CLL) is classified by one of two cytologic staging systems, which known as Rai Classification and Binet Staging, respectively.